The present invention relates generally to a heating and cooling system, and more particularly to a fuel-fired heating and cooling system which is energy-efficient on both the cooling mode of operation and the heating mode of operation.
A variety of heat-powered heating and cooling systems for buildings has been provided by the prior art. Such systems typically include a vapor power circuit such as a steam power circuit having a prime mover expander, such as a turbine. The prime mover expander drives a compressor within a refrigeration circuit which is used as a reversible heat pump for heating and cooling the building.
One such prior art system, as shown in U.S. Pat. No. 3,400,554, utilizes the rejected heat from the vapor power circuit prime mover expander to supplement the heat furnished by the reversible refrigeration circuit when the system is on the heating mode. Another prior art system, as shown in U.S. Pat. No. 3,487,655, utilizes the prime mover expander to drive an alternator which provides electrical power for an electric motor-driven compressor and for the associated electric motor-driven pump fans.
The present invention departs from these and other prior art air heating and cooling systems by providing an air heating and cooling system having series heat exchange for refrigeration and heat engine power circuits both inside the building and outside the building. The system includes an expansion-type refrigeration circuit having a compressor, an indoor heat exchanger, and an outdoor heat exchanger. The system also includes a heat engine having a heat rejection circuit which includes a source of rejected heat, a primary heat exchanger connected to the source of rejected heat, an evaporator in heat exchange relation with the primary heat exchanger, an indoor heat exchanger, and an outdoor heat exchanger. The two series indoor heat exchangers and the two series outdoor heat exchangers are arranged with the refrigeration circuit heat exchangers upstream in the air flow path of the heat engine heat rejection heat exchangers. A first fan arrangement conducts air across the indoor heat exchangers and a second fan arrangement conducts air across the outdoor heat exchangers.
When the system is in a heating mode of operation, the indoor refrigeration circuit heat exchanger serves as a condenser to provide one stage of heating for the indoor air, and the indoor heat engine heat rejection circuit heat exchanger receives the rejected heat from the heat engine to provide a second stage of heating for the indoor air. The outdoor heat exchanger of the heat engine heat rejection circuit does not receive rejected heat from the heat engine during the heating mode.
When the system is on the cooling mode of operation, the indoor refrigeration circuit heat exchanger serves as an evaporator to cool the indoor air, and the rejected heat from the heat engine is directed away from the indoor heat rejection circuit heat exchanger. The outdoor refrigeration circuit heat exchanger functions as a condenser, and the rejected heat from the heat engine is conveyed to the outdoor heat rejection circuit heat exchanger during the cooling mode.
The heat engine also drives an alternator which provides electrical power to the first and second fan arrangements. As the speed of the heat engine is increased, the electrical power output of the alternator increases to increase the speed of the fans and thereby increase air flow across both the indoor and outdoor heat exchangers.
During very cold weather, vapor from a vapor generator is incrementally injected directly into the heat engine heat rejection circuit to increase the heating capacity of the system and avoid undesirable compressor operating conditions.
The use of the primary heat exchanger and evaporator and indoor and outdoor heat exchangers in the heat engine heat rejection circuit produces a number of advantages for the system. The fluid used in the evaporator and indoor and outdoor heat exchangers of the heat rejection circuit can be in the same fluid which is used in the indoor and outdoor heat exchangers of the refrigeration circuit. The hardware in the system is thus simplified, since smaller hardware can be used than would be required if steam and water vapor were circulated in the heat rejection circuit indoor and outdoor heat exchangers. Additionally, a common valve can be used for switching from the heating mode to the cooling mode on both the heat rejection circuit and the refrigeration circuit, since any normal leakage in the valve from one of the circuits to the other circuit is not objectionable when the same fluid is used in both circuits. Still further, freeze protection is not required for the indoor and outdoor heat exchangers of the heat rejection circuit when a fluid having a very low freezing point is used in place of water and steam.
According to another aspect of the invention, the outlets of the outdoor heat exchangers are connected through a back pressure regulator, and the outlets of the indoor heat exchangers are also connected through a back pressure regulator when the same fluid is used in both indoor heat exchangers and in both outdoor heat exchangers to further simplify the hardware components of the system. Additionally, the inlet sides of the outdoor heat exchangers are connected by a valve, and the inlet sides of the indoor heat exchangers are connected by another valve to permit both indoor heat exchangers or both outdoor heat exchangers to be used as the evaporator for the refrigeration circuit.
Although the system is described herein with reference to indoor and outdoor air, the system can also be used with indoor and outdoor fluids other than air, such as water or brine. Additionally, the indoor and outdoor fluids need not be the same fluid, for example when the indoor fluid is air and the outdoor fluid is ocean brine.